Densified battery electrodes and methods thereof

ABSTRACT

In an aspect, a Li-ion cell may comprise a densified electrode exhibiting an areal capacity loading of more than about 4 mAh/cm 2 . For example, the densified electrode may a first electrode part arranged on a current collector and a second electrode part on top of the first electrode part, the second electrode part of the at least one densified electrode having a higher porosity than the first electrode part of the at least one densified electrode. In some designs, the densified electrode may be fabricated by densifying electrode layers via a pressure roller while maintaining a contacting part of the pressure roller at a temperature that is less than a temperature of the second electrode part. In some designs, the applied pressure is a time-varying (e.g., frequency modulated) pressure. In some designs, a drying time for a slurry to produce the densified electrode may range from around 1-120 seconds.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application for patent claims the benefit of U.S.Provisional Application No. 62/852,151, entitled “METHODS FOR IMPROVINGPERFORMANCE OF THICK, VOLUMETRIC ENERGY-DENSE BATTERY ELECTRODES ANDCOMPOSITIONS OF BATTERY CELLS COMPRISING SAME,” filed May 23, 2019,which is expressly incorporated herein by reference in its entirety.

BACKGROUND Field

Embodiments of the present disclosure relate generally to energy storagedevices, and more particularly to battery technology and the like.

Background

Owing in part to their relatively high energy densities, relatively highspecific energy, light weight, and potential for long lifetimes,advanced rechargeable and primary (not rechargeable) batteries aredesirable for a wide range of wearables, portable consumer electronics,electric vehicles, grid storage, aerospace and other importantapplications.

However, despite the increasing commercial prevalence of rechargeableLi-ion batteries, further development of these batteries is needed,particularly for potential applications in battery-powered electricalvehicles, consumer electronics and aerospace applications, among others.Fabrication of thicker and denser electrodes with a low concentration ofdefects and well controlled porosity is important for reducing batterycost and increasing volumetric and gravimetric battery energy densities.Unfortunately, conventional routes to produce such electrodes typicallyfail to achieve the desired level of porosity control, often requireexcessive efforts and costs, and often exhibit undesirably low rateperformance and stability.

Accordingly, there remains a need for improved battery cells,components, and other related materials and manufacturing processes.

SUMMARY

Embodiments disclosed herein address the above stated needs by providingimproved battery components, improved batteries made therefrom, andmethods of making and using the same.

An embodiment of the present disclosure is directed to a Li-ion battery,comprising anode and cathode electrodes an electrolyte ionicallycoupling the anode and the cathode electrodes, and a separatorelectrically separating the anode and the cathode electrodes, whereinthe anode and cathode electrodes comprise at least one densifiedelectrode exhibiting an areal capacity loading of more than about 4mAh/cm² and comprising a first electrode part arranged on a currentcollector and a second electrode part on top of the first electrodepart, the second electrode part of the at least one densified electrodehaving a higher porosity than the first electrode part of the at leastone densified electrode.

Another embodiment of the present disclosure is directed to a densifiedelectrode for a Li-ion battery, comprising a first electrode partarranged on a current collector, and a second electrode part arranged ontop of the first electrode part, the second electrode part having ahigher porosity than the bottom electrode part, wherein the densifiedelectrode exhibits an areal capacity loading in excess of about 4mAh/cm².

Another embodiment of the present disclosure is directed to a method offabricating an electrode, comprising coating a current collector with aset of electrode layers so as to define a first electrode part arrangedon the current collector and a second electrode part arranged on top ofthe first electrode part, and densifying the set of electrode layersafter the coating via a pressure roller to produce a densified electrodewhile maintaining a contacting part of the pressure roller at atemperature that is less than a temperature of the second electrodepart.

Another embodiment of the present disclosure is directed to a method offabricating an electrode for a Li-ion battery, comprising coating acurrent collector with one or more electrode layers, and densifying theone or more electrode layers after the coating via applying atime-varying pressure to produce a densified electrode.

Another embodiment of the present disclosure is directed to a method offabricating an electrode for a Li-ion battery, comprising coating acurrent collector with an electrode slurry comprising at least activeelectrode particles and a solvent, and drying, during a drying time, theelectrode slurry to produce an at least partially dried electrodecoating, wherein the drying time ranges from around 1 to around 120seconds.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are presented to aid in the description ofembodiments of the invention and are provided solely for illustration ofthe embodiments and not limitation thereof.

FIG. 1 illustrates an example (e.g., Li-ion) battery in which thecomponents, materials, methods, and other techniques described herein,or combinations thereof, may be applied according to variousembodiments.

FIG. 2 illustrates an electrode produced in accordance with anembodiment of the present disclosure.

FIG. 3 illustrates an electrode produced in accordance with anotherembodiment of the present disclosure.

FIG. 4 illustrates a process of fabricating an electrode in accordancewith an embodiment of the disclosure.

FIG. 5 illustrates an electrode produced in accordance with anotherembodiment of the present disclosure.

FIG. 6 illustrates an electrode produced in accordance with anotherembodiment of the present disclosure.

FIGS. 7A-7B illustrate a densified electrode before and aftersacrificial material removal in accordance with an embodiment of thedisclosure.

FIGS. 8A-8B illustrate an electrode dried in accordance with someembodiments of the present disclosure

FIG. 9 illustrates an electrode dried in accordance with anotherembodiment of the present disclosure.

FIG. 10 illustrates a method of producing a cell in accordance with anembodiment of the present disclosure.

FIGS. 11A-11E illustrate a building block of a cell with thick, highloading electrodes produced staring from a slurry cast on a currentcollector, before and after being partially dried to form asolvent-comprising electrode, before and after being densified to form asolvent-comprising dense electrode, before and after being assembledinto a stack with a solvent-comprising dense electrode, before and afterbeing filled with electrolyte in accordance with an embodiment of thedisclosure.

DETAILED DESCRIPTION

Aspects of the present invention are disclosed in the followingdescription and related drawings directed to specific embodiments of theinvention. The term “embodiments of the invention” does not require thatall embodiments of the invention include the discussed feature,advantage, process, or mode of operation, and alternate embodiments maybe devised without departing from the scope of the invention.Additionally, well-known elements of the invention may not be describedin detail or may be omitted so as not to obscure other, more relevantdetails. Further, the terminology of “at least partially” is intendedfor interpretation as “partially, substantially or completely”.

While the description below may describe certain examples in the contextof rechargeable and primary Li and Li-ion batteries (for brevity andconvenience, and because of the current popularity of Li technology), itwill be appreciated that various aspects may be applicable to otherrechargeable and primary batteries (such as Na-ion, Mg-ion, K-ion,Ca-ion, Al-ion and other metal-ion batteries, anion-ion (e.g., F-ion)batteries, dual ion batteries, alkaline batteries, acid batteries, solidstate batteries, etc.) as well as electrochemical capacitors (includingdouble layer capacitors and so-called supercapacitors) with variouselectrolytes and various hybrid devices.

While the description below may describe certain examples of thematerial formulations for several specific types of cathode or anodematerials, it will be appreciated that various aspects may be applicableto various other electrode materials.

While the description below may describe certain embodiments in thecontext of preparation of porous electrodes for energy storage devices,it will be appreciated that various aspects may be applicable forpreparation of other porous bodies comprised of compacted individualparticles.

While the description below may describe certain embodiments in thecontext of preparation of porous electrodes comprising polymer binder,it will be appreciated that various aspects may be applicable to porouselectrodes (and other porous bodies) comprising other types of binder(s)or mixture of binders or not comprising binder at all.

Any numerical range described herein with respect to any embodiment ofthe present invention is intended not only to define the upper and lowerbounds of the associated numerical range, but also as an implicitdisclosure of each discrete value within that range in units orincrements that are consistent with the level of precision by which theupper and lower bounds are characterized. For example, a numericaldistance range from 50 μm to 1200 μm (i.e., a level of precision inunits or increments of ones) encompasses (in μm) a set of [50, 51, 52,43, . . . , 1199, 1200], as if the intervening numbers 51 through 1199in units or increments of ones were expressly disclosed. In anotherexample, a numerical percentage range from 0.01% to 10.00% (i.e., alevel of precision in units or increments of hundredths) encompasses (in%) a set of [0.01, 0.02, 0.03, . . . , 9.99, 10.00], as if theintervening numbers between 0.02 and 9.99 in units or increments ofhundredths were expressly disclosed. Hence, any of the interveningnumbers encompassed by any disclosed numerical range are intended to beinterpreted as if those intervening numbers had been disclosedexpressly, and any such intervening number may thereby constitute itsown upper and/or lower bound of a sub-range that falls inside of thebroader range. Each sub-range (e.g., each range that includes at leastone intervening number from the broader range as an upper and/or lowerbound) is thereby intended to be interpreted as being implicitlydisclosed by virtue of the express disclosure of the broader range.

Some examples below characterize numerical values using approximations(e.g., terms such as “about”, “around”, “approximately”, “˜”, etc.). Insome designs, such approximations may be accurate either to a degreecommensurate with the relevant instrumentation (e.g., caliper orthickness gauge or pressure gauge, etc.) for measuring the associatedvalue, or to a degree to which that value would be rounded at anassociated level of precision (e.g., whichever is greater). For example,“about 4” may encompass any value between 3.5 and 4.5, “about 4.0” mayencompass any value between 3.95 and 4.05″, “about 4.00” may encompassany value between 3.995 and 4.005, and so on.

FIG. 1 illustrates an example metal-ion (e.g., Li-ion or Na-ion) batteryin which the components, materials, methods, and other techniquesdescribed herein, or combinations thereof, may be applied according tovarious embodiments. A cylindrical battery is shown here forillustration purposes, but other types of arrangements, includingprismatic or pouch (laminate-type) or coin-type batteries, may also beused as desired. The example battery 100 includes a negative anode 102,a positive cathode 103, a separator 104 interposed between the anode 102and the cathode 103, an electrolyte (not shown) impregnating theseparator 104, a battery case 105, and a sealing member 106 sealing thebattery case 105.

Conventional electrodes utilized in Li-ion or Na-ion batteries may beproduced by (i) formation of a slurry comprising active materials,conductive additives, binder solutions and, in some cases, surfactant orother functional additives; (ii) casting the slurry onto a metal foil(e.g., Cu foil for most Li-ion battery anodes and Al foil for mostLi-ion battery cathodes and for most Na-ion battery anodes andcathodes); (iii) drying the casted electrodes to completely evaporatethe solvent; and (iv) calendaring (densification) of the driedelectrodes by uniform pressure rolling. In case of thicker electrodesthat exhibit relatively high areal capacity (e.g., above about 4mA/cm²), calendaring may be conducted multiple times in order to achievelow porosity and a high volume-fraction of active materials and thushigh volumetric capacity (e.g., above about 600 mAh/cm³).

Batteries may be produced by (i) assembling/stacking (or rolling intoso-called jelly roll) the anode/separator/cathode/separator sandwich;(ii) inserting the stack (or jelly roll) into the battery housing(casing); (iii) filling electrolyte into the pores of the electrodes andthe separator (and also into the remaining areas of the casing)—oftenunder vacuum; (iv) pre-sealing the battery cell (often under vacuum);(v) conducting so-called “formation” cycle(s) where the battery isslowly charged and discharged (e.g., one or more times); (vi) removingformed gases, sealing the cell, testing the cell for quality andshipping quality cells to customers.

Both liquid and solid electrolytes may be used for the designs herein.Exemplary liquid electrolytes for Li- or Na-based batteries of this typemay be composed of a single Li or Na salt (such as LiPF₆ for Li-ionbatteries and NaPF₆ or NaClO₄ salts for Na-ion batteries) in a mixtureof organic solvents (such as a mixture of carbonates and/or othersuitable solvents). Other suitable organic solvents include nitriles,esters, sulfones, sulfoxides, phosphorous-based solvents, silicon-basedsolvents, ethers, and others. In some designs, such solvents may bemodified (e.g., be sulfonated or fluorinated). In some designs, theelectrolytes may also comprise ionic liquids (in some designs, neutralionic liquids; in other designs, acidic and basic ionic liquids). Insome designs, the electrolytes may also comprise mixtures of varioussalts (e.g., mixtures of several Li salts or mixtures of Li and non-Lisalts for rechargeable Li and Li-ion batteries).

In the case of aqueous Li-ion (or aqueous Na-ion, K-ion, Ca-ion, etc.)batteries, electrolytes may include a solution (e.g., aqueous solutionor mixed aqueous-organic solution) of inorganic Li (or Na, K, Ca, etc.)salt(s) (such as Li₂SO₄, LiNO₃, LiCl, LiBr, Li₃PO₄, H₂LiO₄P, C₂F₃LO₂,C₂F₃LiO₃S, Na₂₃Se, Na₂SO₄, Na₂O₇Si₃, Na₃O₉P₃, C₂F₃NaO₂, etc.). Theseelectrolytes may also comprise solutions of organic Li (or Na, K, Ca,etc.) salts, such as (listed with respect to Li for brevity) metal saltsof carboxylic acids (such as HCOOLi, CH₃COOLi, CH₃CH₂COOLi,CH₃(CH₂)₂COOLi, CH₃(CH₂)₃COOLi, CH₃(CH₂)₄COOLi, CH₃(CH₂)₅COOLi,CH₃(CH₂)₆COOLi, CH₃(CH₂)₇COOLi, CH₃(CH₂)₈COOLi, CH₃(CH₂)₉COOLi,CH₃(CH₂)₁₀COOLi, CH₃(CH₂)₁₁COOLi, CH₃(CH₂)₁₂COOLi, CH₃(CH₂)₁₃COOLi,CH₃(CH₂)₁₄COOLi, CH₃(CH₂)₁₅COOLi, CH₃(CH₂)₁₆COOLi, CH₃(CH₂)₁₇COOLi,CH₃(CH₂)₁₈COOLi and others with the formula CH₃(CH₂)_(x)COOLi, where xranges up to 50); metal salts of sulfonic acids (e.g., RS(═O)₂—OH, whereR is a metal salt of an organic radical, such as a CH₃SO₃Li,CH₃CH₂SO₃Li, C₆H₅SO₃Li, CH₃C₆H₄SO₃Li, CF₃SO₃Li, [CH₂CH(C₆H₄)SO₃Li]_(n)and others) and various other organometallic reagents (such as variousorganolithium reagents), to name a few. In some designs, such solutionsmay also comprise mixtures of inorganic and organic salts, various othersalt mixtures (for example, a mixture of a Li salt and a salt of non-Limetals and semimetals), and, in some cases, hydroxide(s) (such as LiOH,NaOH, KOH, Ca(OH)₂, etc.), and, in some cases, acids (including organicacids). In some designs, such aqueous electrolytes may also compriseneutral or acidic or basic ionic liquids (from approximately 0.00001 wt.% to approximately 40 wt. % relative to the total weight ofelectrolyte). In some designs, such “aqueous” (or water containing)electrolytes may also comprise organic solvents (from approximately0.00001 wt. % to approximately 40 wt. % relative to the total weight ofelectrolyte), in addition to water. Illustrative examples of suitableorganic solvents may include carbonates (e.g., propylene carbonate,ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methylcarbonate, fluoroethylene carbonate, vinylene carbonate, and others),various nitriles (e.g., acetonitrile, etc.), various esters, varioussulfones (e.g., propane sulfone, etc.), various sultones, varioussulfoxides, various phosphorous-based solvents, various silicon-basedsolvents, various ethers, and others.

The most common salt used in a Li-ion battery electrolyte, for example,is LiPF₆, while less common salts include lithium tetrafluoroborate(LiBF₄), lithium perchlorate (LiClO₄), lithium bis(oxalato)borate(LiB(C₂O₄)₂), lithium difluoro(oxalate)borate (LiBF₂(C₂O₄)), variouslithium imides (such as SO₂FN⁻ (Li⁺)SO₂F, CF₃SO₂N⁻(Li⁺)SO₂CF₃,CF₃CF₂SO₂N⁻(Li⁺)SO₂CF₃, CF₃CF₂SO₂N⁻(Li⁺)SO₂CF₂CF₃,CF₃SO₂N⁻(Li⁺)SO₂CF₂OCF₃, CF₃OCF₂SO₂N⁻(Li⁺)SO₂CF₂OCF₃,C₆F₅SO₂N⁻(Li⁺)SO₂CF₃, C₆F₅SO₂N⁻(Li⁺)SO₂C₆F₅ or CF₃SO₂N⁻(Li⁺)SO₂PhCF₃,and others), and others. Electrolytes for Mg-ion, K-ion, Ca-ion, andAl-ion batteries are often more exotic as these batteries are in earlierstages of development. In some designs, such electrolytes may comprisedifferent salts and solvents (in some cases, ionic liquids may replaceorganic solvents for certain applications).

In some designs, some electrolytes in aqueous batteries (such asalkaline batteries, including nickel-metal hydride batteries) maycomprise an alkaline solution (for example, a mixture of KOH and LiOHsolutions). In some designs, electrolytes in aqueous batteries (such aslead acid batteries) may comprise an acidic aqueous solution (forexample, H₂SO₄ aqueous solution). In some designs, electrolytes inaqueous batteries may comprise an organic solvent as an additive. Insome designs, electrolytes in aqueous batteries may comprise two or moreorganic solvent(s) or ionic liquid(s) as additive(s) or substantialcomponents of the electrolyte.

Certain conventional cathode materials utilized in Li-ion batteries areof an intercalation-type. In such cathodes, metal ions are intercalatedinto and occupy the interstitial positions of such materials during thecharge or discharge of a battery. Such cathodes typically experiencevery small volume changes when used in electrodes. Such cathodematerials also may exhibit high density (e.g., about 3.8-6 g/cm³ at theindividual particle basis). Illustrative examples of suchintercalation-type cathode materials include but are not limited tolithium cobalt oxide (LCO), lithium nickel cobalt aluminum oxide (NCA),lithium nickel manganese cobalt oxide (NMC), lithium manganese oxide(LMO), lithium nickel oxide (LNO), high voltage spinel, such as lithiummanganese nickel oxide (LiMn_(1.5)Ni_(0.5)O₄ or LMNO), lithium metal(e.g., iron or cobalt or nickel or manganese or mixture of these andother metals) phosphate (LMP such as LFP, LCP, LNP, LNP, etc.), lithiummetal silicates (Li₂MSiO₄, where M could be Ni, Co, Mn, Fe, variousmixture of these and other metals, etc.), various other intercalationcathode materials including those that comprise surface coatings orexhibit gradient composition within individual particles, among others.Polyvinylidene fluoride, or polyvinylidene difluoride (PVDF), is themost common binder used in these electrodes. Carbon black and carbonnanotubes are the most common conductive additive used.

Conversion-type cathode materials for rechargeable Li-ion or Libatteries may offer higher energy density, higher specific energy, orhigher specific or volumetric capacities compared to intercalation-typecathode materials. For example, fluoride-based cathodes may offeroutstanding technological potential due to their very high capacities,in some cases exceeding about 300 mAh/g (greater than about 1200 mAh/cm³at the electrode level). For example, in a Li-free state, FeF₃ offers atheoretical specific capacity of 712 mAh/g; FeF₂ offers a theoreticalspecific capacity of 571 mAh/g; MnF₃ offers a theoretical specificcapacity of 719 mAh/g; CuF₂ offers a theoretical specific capacity of528 mAh/g; NiF₂ offers a theoretical specific capacity of 554 mAh/g;PbF₂ offers a theoretical specific capacity of 219 mAh/g; BiF₃ offers atheoretical specific capacity of 302 mAh/g; BiF₅ offers a theoreticalspecific capacity of 441 mAh/g; SnF₂ offers a theoretical specificcapacity of 342 mAh/g; SnF₄ offers a theoretical specific capacity of551 mAh/g; SbF₃ offers a theoretical specific capacity of 450 mAh/g;SbF₅ offers a theoretical specific capacity of 618 mAh/g; CdF₂ offers atheoretical specific capacity of 356 mAh/g; and ZnF₂ offers atheoretical specific capacity of 519 mAh/g. Mixtures (for example, inthe form of alloys) of fluorides may offer a theoretical capacityapproximately calculated according to the rule of mixtures. In somedesigns, the use of mixed metal fluorides may sometimes be advantageous(e.g., may offer higher rates, lower resistance, higher practicalcapacity, or longer stability). In a fully lithiated state, metalfluorides convert to a composite comprising a mixture of metal and LiFclusters (or nanoparticles). Examples of the overall reversiblereactions of the conversion-type metal fluoride cathodes may include2Li+CuF₂↔2LiF+Cu for CuF₂-based cathodes or 3Li+FeF₃↔3LiF+Fe forFeF₃-based cathodes or 2Li+NiF₂↔2LiF+Ni for NiF₂-based cathodes, etc.).It will be appreciated that metal fluoride-based cathodes may beprepared in both Li-free or partially lithiated or fully lithiatedstates.

Another example of a promising conversion-type Li-ion battery cathode(or, in some cases, anode) material is sulfur (S) (in a Li-free state)or lithium sulfide (Li₂S, in a fully lithiated state). In order toreduce dissolution of active material during cycling, to improveelectrical conductivity, or to improve mechanical stability of S/Li₂Selectrodes in some designs, one may advantageously utilize porous S,Li₂S, porous S—C (nano)composites, Li₂S—C(nano)composites, Li₂S-metaloxide (nano)composites, Li₂S—C-metal oxide (nano)composites,Li₂S—C-metal sulfide (nano)composites, Li₂S-metal sulfide(nano)composites, Li₂S—C-mixed metal oxide (nano)composites,Li₂S—C-mixed metal sulfide (nano)composites, porous S-polymer(nano)composites, or other composites or (nano)composites comprising Sor Li₂S, or both. In some designs, such (nano)composites mayadvantageously comprise conductive carbon. In some designs, such(nano)composites may advantageously comprise metal oxides or mixed metaloxides. In some designs, such (nano)composites may advantageouslycomprise metal sulfides or mixed metal sulfides. In some examples, mixedmetal oxides or mixed metal sulfides may comprise lithium metal. In someexamples, mixed metal oxides may comprise titanium metal. In someexamples, lithium-comprising metal oxides or metal sulfides may exhibita layered structure. In some examples, metal oxides or mixed metaloxides or metal sulfides or mixed metal sulfides may advantageously beboth ionically and electrically conductive. In some examples, variousother intercalation-type active materials may be utilized instead of orin addition to metal oxides or metal sulfides. In some designs, such anintercalation-type active material exhibits charge storage (e.g., Liinsertion/extraction capacity) in the potential range close to that of Sor Li₂S (e.g., within about 1.5-3.8 V vs. Li/Li⁺).

Unfortunately, many conversion-type electrodes used in Li-ion batteriessuffer from performance limitations. Formation of (nano)composites may,at least partially, overcome such limitations. For example,(nano)composites in some designs may offer reduced voltage hysteresis,improved capacity utilization, improved rate performance, improvedmechanical and sometimes improved electrochemical stability, reducedvolume changes, and/or other positive attributes. Examples of suchcomposite cathode materials include, but are not limited to, LiF—Cu—Fe—Cnanocomposites, LiF—Cu—CuO—C nanocomposites, LiF—Cu—Fe—CuO—Cnanocomposites, LiF—Cu—Fe—CuO—Fe₂O₃—C nanocomposites, FeF₂—Cnanocomposites, FeF₂—Fe₂O₃—C nanocomposites, FeF₃—C nanocomposites,FeF₃—Fe₂O₃—C nanocomposites, CuF₂—C nanocomposites, CuO—CuF₂—Cnanocomposites, LiF—Cu—C nanocomposites, LiF—Cu—C-polymernanocomposites, LiF—Cu—CuO—C-polymer nanocomposites,LiF—Cu-metal-polymer nanocomposites, and many other porousnanocomposites comprising LiF, FeF₃, FeF₂, MnF₃, CuF₂, NiF₂, PbF₂, BiF₃,BiF₅, CoF₂, SnF₂, SnF₄, SbF₃, SbF₅, CdF₂, or ZnF₂, or other metalfluorides or their alloys or mixtures and optionally comprising metaloxides and their alloys or mixtures. In some examples, metal sulfides ormixed metal sulfides may be used instead of or in addition to metaloxides in such (nano)composites. In some examples, metal fluoridenanoparticles may be infiltrated into the pores of porous carbon (forexample, into the pores of activated carbon particles) to form thesemetal-fluoride-C nanocomposites. In some examples, such compositeparticles may also comprise metal oxides (including mixed metal oxidesor metal oxyfluorides or mixed metal oxyfluorides) or metal sulfides(including mixed metal sulfides). In some examples, mixed metal oxidesor mixed metal sulfides may comprise lithium metal. In some examples,lithium-comprising metal oxides or metal sulfides may exhibit a layeredstructure. In some examples, metal oxides or mixed metal oxides or metalsulfides or mixed metal sulfides may advantageously be both ionicallyand electrically conductive.

In some examples, various intercalation-type active materials may beutilized instead of or in addition to metal oxides or metal sulfides. Insome designs, such an intercalation-type active material exhibits chargestorage (e.g., Li insertion/extraction capacity) in the same potentialrange as metal fluorides or in the nearby potential range (e.g., withinabout 1.5-4.2 V vs. Li/Li⁺). In some examples, such metal oxides mayencase the metal fluorides and advantageously prevent (or significantlyreduce) direct contact of metal fluorides (or oxyfluorides) with liquidelectrolytes (e.g., in order to reduce or prevent metal corrosion anddissolution during cycling). In some examples, nanocomposite particlesmay comprise carbon shells or carbon coatings. In some designs, such acoating may enhance electrical conductivity of the particles and mayalso prevent (or help to reduce) undesirable direct contact of metalfluorides (or oxyfluorides) with liquid electrolytes. In some designs,such fluoride-comprising (nano)composite particles may be used innonlithiated, fully lithiated and partially lithiated states.

Conventional anode materials utilized in Li-ion batteries are also of anintercalation-type. The most common anode material in conventionalintercalation-type Li-ion batteries is synthetic or natural graphite orsoft carbon or hard carbon or graphite-comprising composites, mixture ofcarbons (including graphites), lithium titanium oxides (LTO), lithiumvanadium oxides (LVO) and others. PVDF, carboxymethyl cellulose (CMC),alginic acid and their various salts (e.g., often Na or Li, etc.),polyacrylic acid (PAA) and their various salts (e.g., often Na or Li,etc.) are some of the most common binders used in these electrodes,although other binders may also be successfully used. Carbon black andcarbon nanotubes are some of the most common conductive additive used inthese electrodes.

Alloying-type anode materials for use in Li-ion batteries offer highergravimetric and volumetric capacities compared to intercalation-typeanodes. For example, silicon (Si) offers approximately 10 times highergravimetric capacity and approximately 3 times higher volumetriccapacity compared to an intercalation-type graphite (or graphite-like)anode. However, Si suffers from significant volume expansion during Liinsertion (up to approximately 300 vol. %) and thus may induce thicknesschanges and mechanical failure of Si-comprising anodes in some designs.In addition, Si (and some Li—Si alloy compounds that may form duringlithiation of Si) suffers from relatively low electrical conductivityand relatively low ionic (Li-ion) conductivity. Electronic and ionicconductivity of Si is lower than that of graphite. In some designs,formation of (nano)composite Si-comprising particles (including, but notlimited to Si-carbon composites, Si-metal composites, Si-polymercomposites, Si-metal-polymer composites, Si-carbon-polymer composites,Si-metal-carbon-polymer composites, Si-ceramic composites, or othertypes of porous composites comprising nanostructured Si ornanostructured or nano-sized Si particles of various shapes and forms)and their combinations may reduce volume changes during Li-ion insertionand extraction, which, in turn, may lead to better cycle stability inrechargeable Li-ion cells. In addition to Si-comprising nanocompositeanodes, other examples of such nanocomposite anodes comprisingalloying-type active materials include, but are not limited to, thosethat comprise germanium, antimony, aluminum, magnesium, zinc, gallium,arsenic, phosphorous, silver, cadmium, indium, tin, lead, bismuth, theiralloys, and others. In addition to (nano)composite anodes comprisingalloying-type active materials, other interesting types of high capacity(nano)composite anodes may comprise metal oxides (including, but notlimited to silicon oxide, lithium oxide, various sub-oxides, etc.),metal nitrides (including, but not limited to silicon nitride, varioussub-nitrides, etc.), metal oxy-nitrides (including, but not limited tosilicon oxy-nitrides), metal phosphides (including, but not limited tolithium phosphide and other metal phosphides and sub-phosphides), metalhydrides, and others as well as their various mixtures, alloys andcombinations.

Organic solution-soluble or water-soluble binders are commonly used inelectrode construction. In some designs, the amount of binder may beoptimized for: a particular electrode active material (and its particlesize distribution, specific surface area, shape, density, surfacechemistry and/or other material parameters), conductive additivestype(s) (and their particle size distribution, specific surface area,shape, density, surface chemistry and/or other material parameters) andrelative amount, electrode density, capacity loading, final electrodethickness, calendaring (pressure rolling) conditions and/or otherparameters. Excessive binder content in the electrodes (both anodes andcathodes), for example, may undesirably reduce volumetric capacity ofthe electrodes or reduce electrode porosity and increase tortuosity,thus negatively affecting energy density or power density or both. Insome designs, excessive binder content and insufficient remaining porevolume may also induce premature failure due to excessively increasedresistance growing during cycling. Finally, higher binder content mayincrease total material costs. Too little binder, on the other hand, mayprovide insufficient mechanical robustness to the electrode and inducepremature electrode failure during cycling or delamination from thecurrent collector in some designs. While the optimum content may varygreatly, electrodes in accordance with some designs may comprise fromaround 0.15 wt. % to around 15 wt. % of the binder.

In some designs, carbon nanotubes (e.g., multiwalled, double-walled,single-walled, etc.), carbon nanofibers and other one dimensional (1D)carbon materials, exfoliated graphite, graphene, graphene oxide (e.g.,multiwalled, double-walled, single-walled, etc.) and other twodimensional (2D) carbon materials, carbon black or carbon onions andother zero dimensional (0D) carbon materials as well as variousdendritic carbon and other structures three dimensional (3D) carbonmaterials may be effectively used as conductive carbon additives inelectrode construction. In some designs, conductive oxide, carbide ormetal(s) in the form of 0D, 1D and 2D materials (e.g., nanoparticles,nanofibers or nanoflakes) may be successfully utilized as conductiveadditives. In some designs, conductive additives and active particlesmay have an opposite charge. In some designs, conductive additivesand/or active particles may have functional groups attached to theirsurface. In some designs, heating of the electrode after casting orcalendaring may induce formation of chemical bonds between conductiveadditives and active particles. While the optimum content may varygreatly, electrodes in accordance with some designs may comprise fromaround 0.02 wt. % to around 10 wt. % of the conductive additives. Insome designs, excessive content of conductive additives in theelectrodes (both anodes and cathodes) may undesirably reduce volumetriccapacity of the electrodes or increase pore tortuosity or increase firstcycle losses, thus negatively affecting energy density or power densityor both. Finally, higher content of conductive additives may increasetotal material costs. Too little conductive additives, however, mayprovide insufficient electrical connectivity within the electrode,reduce its mechanical stability and also reduce its power rate andincrease electrode resistance in some designs.

As such, in some designs, it is generally desirable to reduce the amountof binder and conductive additives to the level where one or more otherdesired battery characteristics (e.g., sufficiently good mechanicalstability, sufficiently low resistance, sufficiently high power,sufficiently good adhesion to the current collector foils, etc.) areattained for the desired application and application-specificspecifications. As such, for each cell (with its specific electrolyte,active material type, electrode thickness and areal loadings, etc.), theamounts of both the binder and conductive additives may be optimized forparticular applications. For example, thicker electrodes or electrodeswith higher areal capacity loadings may require a larger fraction ofbinder and additives, which may be undesirable. Some aspects of thepresent disclosure provide means and methodologies to achieve a furtherreduction in the binder content (e.g., in some designs, a reduction inthe conductive carbon additives content as well) without sacrificingimportant battery characteristics. Such reductions may not be feasibleto achieve with conventional electrode fabrication processes (methods),particularly for thicker electrodes with high areal capacity loadings.

Copper or copper-containing/copper-based foil or mesh is typically usedas a current collector for graphite, carbon or Si-based anodes forLi-ion batteries, and typically aluminum foil is typically used as acurrent collector for cathodes for Li-ion batteries and higher voltageanodes (such as LTO, among others). However, other metal currentcollectors, such as based on titanium, nickel, stainless steel, andother metals may similarly be used in some designs.

In some applications, in order to reduce the relative fraction ofinactive materials (e.g., current collector foils, separators, etc.), itmay be highly advantageous to produce relatively thick electrodes (e.g.,in some designs, in the range from about 60 micron to about 1200.0micron; in some designs—in the range from about 60 micron to about 800micron; in some designs—in the range from about 60 micron to about 80micron; in some designs—in the range from about 80 to about 100 micron;in some designs—in the range from about 100 to about 200 micron; in somedesigns—in the range from about 200 to about 400 micron; in somedesigns—in the range from about 400 to about 600 micron; in somedesigns—in the range from about 600 to about 800 micron; in somedesigns—in the range from about 800 to about 1,200.0 micron) that arealso dense (e.g., with the porosity in the electrode (pores betweenactive (e.g., Li ion storing) material particles, conductive additivesand the binder) in the range from about 10 vol. % to about 30 vol. %,or, in some designs, below around 20 vol. % (e.g., about 0 vol. % toabout 20 vol. %) or, in some designs, in the range from about 10 vol. %to about 20 vol. % or, in some designs, in the range from about 20 vol.% to about 30 vol. %). In some designs, depending on the volumetriccapacity of active particles in the electrodes, relative content of thebinder and conductive additives and the porosity, the areal loading ofsuch electrodes may range from about 4.0 to about 1000.0 mAh/cm²; insome designs from about 4.0 to about 6.0 mAh/cm²; in some designs fromabout 6.0 to about 9.0 mAh/cm²; in some designs from about 9.0 to about15.0 mAh/cm²; in some designs from about 15.0 to about 30.0 mAh/cm²; insome designs from about 30.0 to about 60.0 mAh/cm²; in some designs fromabout 60.0 to about 150.0 mAh/cm²; in some designs from about 150.0 toabout 300 mAh/cm²; in some designs from about 300.0 to about 1000.0mAh/cm²).

Lower porosity in the electrode may increase volumetric capacity ofelectrodes and thus battery energy density, which is advantageous insome designs. However, in some designs, too low average porosity mayreduce power density of the batteries (rate performance of electrodes)due to slower transport of Li ions during charging or discharging as theamount of highly ionically conductive electrolyte becomes small. In somedesigns, too high total average porosity may be undesirable because itmay require a larger fraction of relatively expensive electrolyte andbecause it may reduce energy density of the cell. The overall averageporosity in each electrode may be optimized for a particular cell designand application.

In some applications, thicker electrodes may be more difficult todensify than thinner electrodes. In addition, in an example, the thickerthe dense electrodes are, the harder it may be to achieve uniformporosity in the electrode (or, more generally, desired distribution ofthe pore volumes throughout the electrode thickness). Thicker electrodesmay also be harder to dry (or it may take undesirable long) whileavoiding nonuniform stress-induced defects that result in inferior cellperformance. Furthermore, in an example, the thicker the denseelectrodes are, the harder it may be to achieve sufficiently high (for agiven application) power density, sufficiently low (for a givenapplication) resistance; sufficiently high (for a given application)charge rate performance and discharge rate performance of theelectrodes, sufficiently long (for a given application) cycle stability,sufficiently good (for a given application) low temperature performance(e.g., in the temperature range from about minus (−) 70° C. to about −5°C.), sufficiently good (for a given application) adhesion to the currentcollector foils and sufficiently good (for a given application) cyclestability. One or more embodiments of the present disclosure aredirected to overcoming some or all of the above-discussed challengesassociated with making and using dense and thick electrodes whileobtaining substantially improved performance characteristics (e.g.,faster rates, lower total resistance, broader operational temperaturerange, longer cycle stability, etc.).

One conventional procedure to produce dense electrodes involves (i)electrode casting on current collector foils followed by (ii)pressure-rolling (also called “calendaring”) of the casted electrodes toincrease their density. Depending on the application and the tool setup,the diameter of the pressure rolling machine rolls may range from about4″ to about 8″ for laboratory rollers; from about 8″ to about 20″ forthe pilot scale rollers and from about 20″ to about 60″ for very largeindustrial production rollers. In some applications, larger diametersmay result in a more uniform electrode densification. Too large of adiameter, however, may become too expensive to maintain and fix for someapplications. In some designs, the thicker electrodes may be casted inmultiple layers (one on top of another) to attain the desired electrodethickness while minimizing the drying time and drying-inducednonuniformities. In some designs, the pressure rolling may be appliedmultiple times in order to gradually achieve higher density in thickelectrodes.

In conventional pressure rolling (calendaring), the electrodes may beheated in order to reduce viscosity of the binder and achieve denserelectrodes. One conventional procedure involves heating the rollers to asufficiently high temperature (e.g., in the range from about 50° C. toabout 80° C.; in some designs—to higher temperatures) so that when therollers touch the casted electrodes (not heated, initially at near roomtemperature), they transfer heat to the electrodes. This procedureresults in heating the electrodes during calendaring and making thepolymer binder in such electrodes more easily deformable. The initialtemperature difference between the casted electrodes and theelectrode-contacting part of the heated rollers may range from around20° C. or more (e.g., in some designs, from around 20° C. to around 60°C.).

Unfortunately, conventional calendaring procedures may result in theformation of a much denser layer at the top portion of the electrode,which may slow down the ion transport and rate performance of thick anddense electrodes. One or more embodiments of the present disclosure aredirected to overcoming this limitation via the addition of substantiallyuniform pores in the electrodes or making the top portion of anelectrode more porous (as opposite to less porous) than the bottom partof the electrode, greatly enhancing the rate performance and stabilityof such electrodes (e.g., in some designs, electrodes exhibiting anareal capacity loading of more than about 4 mAh/cm²). Similarly, one ormore embodiments of the present disclosure are directed to making thebottom of the electrode (near the current collector foils) denser andbetter adhered to the current collector foils. As used herein, the“bottom” part of the electrode refers to the side of the electrode thatinterfaces with the current collector foils, with the “top” part of theelectrode corresponding to the surface side of the electrode thatinterfaces with the pressure roller.

In one embodiment of the current disclosure, the electrode is preheatedto temperature T1 before entering the calendaring tool so that thetemperature of the calendaring tool rollers T2 is ranging from around120° C. lower than T1 to around 20° C. higher than T1 (e.g., in somedesigns, the T2 may be from around 120° C. to around 80° C. lower thanT1; in some designs, the T2 may be from around 80° C. to around 60° C.lower than T1; in some designs, the T2 may be from around 60° C. toaround 40° C. lower than T1; in some designs, the T2 may be from around40° C. to around 20° C. lower than T1; in some designs, the T2 may befrom around 20° C. lower than T1 to around the same as T1; in somedesigns, the T2 may be from around the same as T1 to around 20° C.higher than T1). In the case where T2 is lower than T1, the temperatureof the top of the electrodes (that touch the roller) may become lowerthan that of the bottom of the electrodes (that is attached to thecurrent collector foil). As a result, the top of the electrode maybecome less prone to deformation and (after calendaring) less dense thanthe bottom of the electrode. In some applications, the higher porosityin the top layer of the thick electrodes may result in significantlyfaster rate performance and substantially lower resistance to iontransport when compared to conventional thick electrodes with the sameaverage porosity. In addition, in some designs, such electrodes may becalendared to a lower total porosity (be denser) and comprise lessaverage binder amount, while exhibiting the same or better rateperformance, the same or better stability and the same of betteradhesion to the current collector as conventional calendered electrodes.

FIG. 2 illustrates an electrode 201 with the initial thickness of oneside t1i and initial temperature T1 is calendered (densified) to thefinal thickness of one side t1f by passing through a pressure-roller202, the surface of which is kept to an average temperature T2 (e.g.,where T2<T1) in accordance with an embodiment of the present disclosure.

In one or more embodiments of the present disclosure, the electrodes areheated nonuniformly prior to (or during) entering the densification(e.g., calendaring) tool so that the bottom portion of the electrodes(near the current collector foils) is heated to higher temperatures thanthe portion of the electrode near the electrode surface. In one example,one may utilize, for example, inductive heating (or, in some designs,resistive heating—through the current collector foils, for example)where the heat is mostly generated at the current collectors and thenthis heat from the current collectors is transported to the electrodes.As a result of the transient heat flow, the bottom portion of theelectrode may attain a substantially higher temperature. In somedesigns, including a larger fraction or more conductive “conductiveadditives” near the bottom of the electrode may similarly enablestronger heating of the bottom (or bottom and central) portion(s) of theelectrode compared to the top portion of the electrode.

In some designs, either DC (direct current) or AC (alternating current)or a combination of AC and DC currents may be utilized to heat thecurrent collector. When the current collector foils are heated by usinga resistive heating (e.g., passing current through the foil), a voltagedrop may take place along the length of the foil in some designs (inother designs, it may, for example, the voltage drop may take place fromone edge of the foil to another edge in a direction perpendicular to thelength of the foil and parallel to the foil plane). In an example, ifcalendaring is conducted roll-to-roll, the foils are heated by aresistive heating and the current primarily flows along the foil length,the voltage drop (potential difference) may be applied, for example,between an initial coating roller(s) and one or more re/wind roller(s),in some designs. In some designs, the current may flow from thedensification tool (e.g., calendaring tool) that is in a direct contactwith the top surface of the electrode through the electrode towards thecurrent collector foil (e.g., in the direction approximatelyperpendicular to the plane of the electrode) in order to heat theelectrode. In this case, in order to more strongly heat a portion of theelectrode near the current collector (bottom portion of the electrode,or central portion if factoring top/bottom electrodes which sandwich thecurrent collector), it may be advantageous for this (bottom) electrodeportion to have the higher resistance (e.g., comprise less conductiveadditives or more binder than the top portion of the electrode) in orderto induce stronger local heating relative to the top part of theelectrode. In some designs, the electric current direction may bereversed as well (e.g., either from the foil towards the top surface ofthe electrode, or from the top surface of the electrode towards thefoil).

In an example, other methods or combinations of methods may similarly beused to achieve a lower temperature of the top of the electrodes duringcalendaring. In some designs, for example, the top layer of theelectrodes may be intentionally cooled (e.g., by contacting a colderobject or by convection/fan, other means, etc.). Accordingly, variousmethodologies may be deployed for making the top of the electrode colderthan the bottom of the electrode (near the current collector foil)during the calendaring in order to reduce the deformation and retain alarger portion of the open pores (e.g., for faster ion transport) in thetop layer of the electrode. In addition, this approach may permit partof the electrode (e.g., near the current collector) to be heated tohigher temperatures and to apply higher average pressure in order toachieve better compaction of the electrode without significant reductionin the electrode rate performance or other important electrodecharacteristics.

FIG. 3 illustrates an electrode 301 with the initial thickness t1i,initial temperature of the top layer of the electrode T1t and theinitial temperature of the bottom layer of the electrode T1b (T1b>T1t)(near the current collector 303) is calendered (densified) by passingthrough a pressure-roller 302, the surface of which is heated to anaverage temperature T2 in accordance with an embodiment of the presentdisclosure. In some designs, it may be advantageous for the T1b to befrom around 10 to around 120° C. higher than T1t. In some designs, thetemperature difference may be smaller than 10° C. but the positiveimpact may be lower (e.g., fewer or smaller resultant pores in the toppart of the electrode, etc.). Similarly, in some designs, thetemperature difference may be larger than 120° C., but such a design maybe more challenging and more expensive to implement, and, in some cases,it may induce formation of undesirable defects or modifications in theelectrodes or the foils. In some designs, T2 may exhibit nearly the sametemperature as T1t. In other designs, T2 may exhibit a lower temperaturethan T1t (e.g., near room temperature) in order to further increasetemperature difference between the top and bottom portion of theelectrode. In some designs, T2 may exhibit a slightly higher temperaturethan T1t.

In some designs, the roller may be actively cooled during rolling inorder to establish a consistently lower temperature than the top of theelectrode. In an example, such active cooling may be provided by meansof water-cooling, air cooling, Peltier cooling, among other means.

In yet another embodiment of the present disclosure, as discussed belowwith respect to FIG. 4, higher porosity in the top electrode layer maybe attained by producing electrodes with variable binder content. Insome designs, such an electrode may be produced by depositing multiplecoatings with slightly different composition on the top of each other.In some designs, for example, the bottom portion of the electrode maycomprise higher fraction of the binder than the top portion of theelectrode and, after calendaring, retain smaller pore volume but providestronger adhesion to the current collector.

FIG. 4 illustrates a process of fabricating an electrode in accordancewith an embodiment of the disclosure. A current collector is firstprovided (401) and then coated (402) with a first electrode layer at acertain thickness and composition (e.g., with specific amount and/ortype or shape distribution or size distribution of active conductiveadditives, specific amount and/or type of binder, specific amount orsize distribution or type of active material particles; specific amountand type of the solvent). In an example, the first electrode layer maydirectly contact the current collector. In an alternative example, oneor more intervening electrode layers may be arranged between the currentcollector and the first electrode layer. The first electrode layer maythen be (optionally) dried (403) and coated (404) with a secondelectrode layer at a certain thickness (e.g., same or different than thefirst electrode layer) and certain (e.g., different than the firstelectrode layer) composition) (404). The second electrode layer may thenbe (optionally) dried (405). Blocks 404 and 405 may then be optionallyrepeated a desired number of times (e.g., 0-100) to achieve a desiredthickness and a desired number of layers of variable composition. Insome designs, each successive electrode layer may vary in terms ofcomposition, while in other designs two or more adjacent (ornon-adjacent) electrode layers may have substantially the samecomposition. Additional stages may also be introduced into the process(densification), if needed. At 406, the final electrode may becalendered (densified) by passing the electrode one or more timesthrough the pressure roller or other mechanism. In some designs, thefinal calendaring/densification stage 406 is conducted after theelectrode is coated on the opposite side of the current collector (e.g.,401-405 are performed separately on each side of the current collector,after which 406 is performed for densifying the electrode on both sidesof the current collector). In some designs, the calendaring may beconducted at intermediate electrode thicknesses (prior to the depositionof the final/top layer in between repetitions of 404-405). In somedesigns, the calendaring may be conducted both at intermediate electrodethicknesses as well as after the final/top layer is added. In somedesigns, the resultant densified electrode at 406 may capacity loadingof more than about 4 mAh/cm².

In one or more embodiments of the present disclosure, it may beadvantageous to use a different shape or different type/composition ofthe binder through the electrode thickness (e.g., in different electrodelayers). For example, it may be advantageous to use more (e.g.,plastically) deformable binder(s) or the binder(s) with a lower glasstransition temperature (or lower melting point) in the part of theelectrode near the current collector (bottom portion) in order to obtainhigher density of the bottom electrode portion and better adhesion tothe current collector. Similarly, it may be advantageous in some designsto use less (e.g., plastically) deformable (e.g., more rigid) binder(s)or the binder(s) with a higher glass transition temperature (or highermelting point) in the part of the electrode near the top surface (topportion) in order to obtain higher porosity and faster rate performancein the electrodes and cells. In an example, some binder(s) within theelectrode may be in the form of dispersion(s) (e.g., nanofibers) andsome binder(s) in the electrode may be in the form of solution(s). Insome designs, it may be advantageous for the bottom portion of theelectrode (near the foils) to comprise (e.g., more of) the solution-typebinder (e.g., CMC solution in water or other aqueous binder solutions ornonaqueous binder solutions) that may form stronger adhesion to thecurrent collector and for the top portion of the electrode to comprise(e.g., more of) the suspension-type binder (e.g., suspension ofcellulose nanofibers or others) that may facilitate faster transport ofelectrolyte (less electrolyte blockage) after calendaring.

After electrode calendaring, a “spring-back” effect (expansion of theelectrode to some level after the initial compaction) may take place.Different types of conductive additives and different amounts ofconductive additives may impact the degree of spring-back. For example,carbon nanotubes or nanofibers used as conductive additives may resultin a larger spring-back amount compared to carbon black conductiveadditives. Similarly, in an example, the larger amounts of nanotubes ornanofibers or, in some cases, larger diameter and/or length of thenanotubes and nanofibers, may result in a larger spring-back amount. Insome designs, different types of nanotubes and nanofibers (e.g.,different microstructures, compositions, etc.) may result in a differentamount of spring-back. In one or more embodiments of the presentdisclosure, the top portion of the electrode may comprise a higherfraction or a different type of conductive additives than the bottomportion in order to result in a larger spring-back in the top electrodeportion (e.g., and thus larger porosity and faster ion transport) aftercalendaring. In a further example, the bottom portion of the electrodemay have a different composition and/or amount of additives to yield asmaller amount of springback so that smaller pore volume and strongeradhesion of the electrode to the current collector may be attained.Furthermore, by attaining relatively average small springback within theelectrode, sufficiently low average electrode porosity and sufficientlyhigh level of electrode smoothness may be attained.

Conventional electrode densification process involves an application ofeither a fixed force/pressure or (e.g., in case of the pressure rolling)a fixed smallest dimension of the gap between the pressure rollers. Suchprocesses may be relatively inefficient such that multiple repetitionsof the pressure rolling procedures may be employed in order to attain adesired low density (sufficiently small porosity), particularly in thickelectrodes. Such repetitions may increase complexity and cost of theelectrode fabrication. Furthermore, such processes may induce undesireddamages to the electrode particles and may still provide insufficientlyhigh average density for certain applications, and some of the largepores in the electrodes remaining there after the traditionalcalendaring/densification.

In one embodiment of the present disclosure, the pressure (in somedesigns, maximum pressure) applied to the electrode may advantageouslybe modulated (e.g., as a sinusoidal function or a square wave functionor triangular wave function or other variable functions; in somedesigns—periodic, in others—aperiodic). The amplitude of the change may,for example, range from around 1% of the maximum pressure (or force) toaround 50% of the maximum pressure (or force). In some designs, theamplitude may also change (e.g., increase; in some designs—gradually)during some period of the pressure application time (e.g., initially orin another time period). In some designs, the pressure may increase anddecrease during different time periods (e.g., increase initially andthen decrease; in some designs—gradually). In some designs, the averagevalue of the applied pressure may also change (e.g., initially increaseor eventually decrease; in some designs—gradually) during some period(s)of the time. A fixed frequency of the pressure modulation may bedefined, whereas in other designs the frequency of the pressuremodulation may vary across a range of frequencies. In an example, theoptimal frequency (or range of frequencies) of a single modulationfunction for a particular application may depend on the properties ofthe electrode, binder and active material, the total electrodedensification time and other factors, but may generally range fromaround 0.1 Hz to around 10 MHz. In some designs, avoiding a range ofsound frequencies (e.g., from around 20 Hz to around 22 kHz) may beadvantageous in terms of minimization of the hearable noise level inelectrode production facilities (e.g., note that care should be taken tomake sure proper personal protection equipment is used in facilitieswith excessive/harmful sound/noise and such use is carefully monitored).In some designs, the frequency of the modulation may change during thedensification process.

In some designs, two or more distinct functions of pressure modulationsmay overlap for overall improved calendaring efficiency. In oneillustrative example, a sinusoidal pressure wave having a relatively lowamplitude (for example, in the range from around to around 0.001% toaround 5% of the maximum applied pressure) of the uncalendared electrodethickness) and a relatively high frequency (for example, in the rangefrom around 22 kHz to around 10 MHz) may overlap with a sinusoidal wavehaving a higher amplitude (e.g., in the range from around to around 5%to around 100% of the maximum applied pressure) and a lower frequency(for example in the range from around 0.1 Hz to around 20 Hz)) toimprove overall densification efficiency.

In some designs, such processes of pressure modulation (application of adynamic load instead) may facilitate a more efficient electrodedensification (e.g., fewer pressure rolling repetitions or lower overallporosity achieved or fewer damaged particles) compared to theconventional process whereby uniform pressure is used. In addition, suchprocesses of pressure modulation (application of a dynamic load) mayfacilitate less damage to the electrode particles, as such particleshave more opportunities to move and adjust their position instead ofcracking at the pressure concentration points.

FIG. 5 illustrates an electrode 501 subjected to a dynamic (variablewith time) pressure 502 during an electrode densification process inaccordance with an embodiment of the disclosure.

In another embodiment of the present disclosure, the smallest separationdistance between the pressure rollers (gap size) applied to theelectrode during pressure rolling (calendaring) may advantageously bemodulated (e.g., as a sinusoidal function or a square wave function or atriangular wave or other variable/dynamic functions which may beperiodic or aperiodic). In some designs, the amplitude of the minimalseparation distance (amplitude of the gap size variations) change may,for example, range from around 0.001% of the maximum (or uncalendared)electrode thickness to around 100% of the maximum (or uncalendared)electrode thickness (in some designs, from around 0.5% of the maximum oruncalendared electrode thickness to around 20% of the maximum oruncalendared electrode thickness). In some designs, the amplitude of theminimal separation distance change may, for example, range from around25% of the average diameter of active electrode particles to around20,000% of an average diameter of active electrode particles (in somedesigns, from around 50% to around 2000%). In some designs, in case ofperiodic functions that define the gap size, their frequency maygenerally range from around 0.1 Hz to around 10 MHz. In some designs,avoiding a range of sound frequencies (e.g., from around 20 Hz to around22 kHz) may be advantageous in terms of the minimization of the noiselevel in electrode production facilities. In some designs, the frequencyof the modulation may change during the densification process.

In some designs, two or more distinct functions of the distance/gapmodulations may overlap for overall improved calendaring efficiency. Inone illustrative example, a sinusoidal wave function having a relativelylow amplitude (e.g., in the range from around to around 0.001% of theuncalendared electrode thickness to around 2% of the uncalendaredelectrode thickness) and a relatively high frequency (for example in therange from around 22 kHz to around 10 MHz) may overlap with a sinusoidalwave having a higher amplitude and a lower frequency (for example in therange from around 0.1 Hz to around 20 Hz)) to improve overalldensification efficiency.

FIG. 6 illustrates an electrode 601 subjected to a dynamic (variablewith time) gap size between pressure rollers 602 during an electrodedensification process in accordance with an embodiment of thedisclosure.

In one or more embodiments of the present disclosure, at least a portionof an electrode (e.g., a thick electrode) may comprise sacrificialmaterial that may be removed (e.g., dissolved or evaporated) from theelectrode after calendaring, thus opening pores in the densifiedelectrode for faster ion transport. In some designs, such a sacrificialmaterial may be introduced in the form of a solid(s) (e.g., powder,including nanopowder) or in the form of a solution during electrodeslurry mixing (e.g., if wet electrode coating technology is used). Incase of dry electrode coating technology, such a sacrificial materialmay be introduced in the form of a solid(s)/powder(s). In some designs,examples of the shape of a solid sacrificial material in the driedelectrode may be: (nano)particles, (nano)fibers, (nano)flakes,(nano)ribbons, various interconnected objects, random shapes, amongother shapes. In some designs, such a sacrificial material may belocated primarily in the top portion of the electrode (e.g., about 5-50%from the top surface) in order to enhance the ion transport whilekeeping the total electrode porosity relatively small after sacrificialmaterial removal. In some designs, the amount of the sacrificialmaterial may range from around 0.01 wt. % to around 10.00 wt. %(relative to the total amount of solids in the dried electrode). In somedesigns, a temperature of the removal of the sacrificial material mayrange from around 0° C. to around 300° C. (in case when the sacrificialmaterial is removed from the electrode by evaporation or by dissolutionin a solvent). In some designs, a suitable composition of thesacrificial material may depend on multiple factors, including thecomposition of the binder, active material, conductive additives,temperature of the electrode casting, temperature of the electrodedrying, use conditions of the electrodes in cells and other factors.Illustrative examples of suitable sacrificial materials may include, butare not limited to: various inorganic or organic salts (e.g., sulfate,thiosulfate, sulfite, nitrate, phosphate, acetate, formate, acetate,succinate, pyruvate, methanesulfonate and many others) of various metals(e.g., of Na, Ca, K, Mg, Li, Sr, Al or other metals) or ammonium,various soluble (e.g., in water or ethanol or acetone) organiccompounds, water miscible (up to about 1-10 vol. %) organic compoundswith a boiling point in the range from around 60 to around 300° C., highfreezing point (e.g., > about 40° C.) solvents (e.g., naphthalene,camphor, lauric acid, phenol, etc.), among many others.

FIGS. 7A-7B illustrate a densified (calendered) electrode 700 before andafter sacrificial material removal in accordance in an embodiment of thedisclosure. In FIG. 7A, the densified (calendered) electrode 700comprises active material 701, conductive additives 702, binder 703 andsacrificial material 704 coated on a current collector foil 705. Forsimplicity, only one side of the electrode is shown in thisillustration. In FIG. 7B, after removing of the sacrificial material704, pores 706 form, which enables faster ion transport in a batterycell.

In yet another embodiment of the present disclosure, it may beadvantageous for the electrode to be coated by a layer comprisingceramic nanofibers (e.g., Al₂O₃ or SiO₂ or MgO or other metal oxides andtheir mixtures or other ceramic nanofibers that are sufficientlyelectrochemically stable in contact with the electrode surface duringbattery operation) prior to (final) calendaring. In some designs, suchnanofibers may comprise Li or Na. In some designs, such nanofibers maybe porous (e.g., with pores in the range from around 0.3 nm to around100 nm). In some designs, such nanofibers may exhibit high Li ionicconductivity in excess of 10⁻⁵ S cm⁻¹ at room temperature (e.g., eitherbecause they become filled with a liquid electrolyte or because they areintrinsically conductive). In some designs, a ceramic nanofiber layermay also comprise some amount of a polymer binder (e.g., in order toimprove their mechanical connectivity to each other) or other functionaladditives. Such a highly porous nanofiber-based coating may not only actas a thin (in some designs, e.g., from around 0.2 micron to around 12micron in thickness) and highly ionically conductive separator, but mayalso adsorb some of the excess binder in the top electrode layer toprevent (or significantly reduce) formation of the dense, ion transportblocking layer in the top portion of the electrode during calendaring.In some designs, instead of nanofibers one may use porous or ionicallyconductive (and thus permeable to electrolyte) particles of other shapes(e.g., spherical, elliptical, random shape, dendritic, planar, etc.). Insome designs, ceramic nanofibers may be electrically conductive orexhibit mixed (electronic and ionic) conductivity (in this case, aseparator or a separator layer would still be needed to electricallyseparate anode in cathode). In some designs, instead of ceramicnanofibers, one may use conductive carbon or conductive metalnanofibers/nanowires/nanotubes, etc.

In yet another embodiment of the present disclosure, it may beadvantageous for the electrode to comprise embedded (e.g.,interconnected) porous tubes that provide fast ion transport. Diameterof such tubes may range, from around 20 nm to around 2000 nm (e.g.,about 2 micron). In some designs, for example, such tubes may form somesort of a truss that could be placed onto a current collector foil priorto filling the spacing between the porous tubes with an electrodeslurry. In some designs, such a truss may be used instead of the currentcollector foil. In some designs, some of the tubes would haveorientation perpendicular to the electrode in order to enhance top tobottom electrolyte transport. In some designs, such porous tubes may bemixed into a slurry (e.g., prior to coating, drying and calendaring). Insome designs, such porous tubes may be made electrically conductive(e.g., based on carbon, conductive oxides, metals, etc.).

In yet another embodiment of the present disclosure, it may beadvantageous for the electrode slurry (and eventually the dry electrode)to comprise active (Li-ion storing) particles or granules with thepolymer binder being (at least partially) chemically attached to suchparticles (or granules) so that during calendaring the binder does notflow away and does not block the pores (e.g., in the top portion) in theelectrode. In some designs, the use of near-spherical granules (e.g.,comprising from around 100 to around 1,000,000 individual particles andhaving dimensions from around 4 to around 400 micron; in some designsfrom around 4 to around 50 micron; in other designs, from around 50 toaround 100 micron; in other designs, from around 100 to around 200micron; in other designs, from around 200 to around 400 micron) insteadof individual particles may also be advantageous as it may enhance thepore size between the granules and prevent (or reduce) pore blockageduring calendaring. In some designs, it may be advantageous to use acombination of granules of different sizes in order to increase thevolumetric capacity of the thick electrode (volumetric packingefficiency of the granules). In other designs, it may also beadvantageous to use substantially uniform granules (e.g., withcoefficient of variables of less than around 20%) in order to produceuniform electrodes with a high degree of ordering and high degree ofuniformity. In some designs, such granulated electrode may utilize verymild calendaring or even no calendaring at all.

In conventional electrode fabrication, wet electrode coatings are driedby slowly moving the wet electrode coatings through large and longfurnaces (typically heated to 60-120° C.) to ensure slow drying (e.g.,within 3-30 min, typically within 4-20 min) on order to avoid formationof cracks (‘mud cracks”) or delamination from the current collector thatmay take place if the top of the electrode is dried first (due to airconvection and due to being directly exposed to radiation), while thebottom of the electrode (near the current collector) is still wet.Longer heating time is typically required for thicker, higher arealloading electrodes. Such slow drying time not only increases productioncosts but may also lead to undesirable distribution of the binder withinthe electrode, where some of the pores within the electrode may becomeblocked by the binder or binder-conductive additive clusters. Thissituation may lead to substantially reduced power performance andstability and other undesirable outcomes. Some aspects of the presentdisclosure provide means and methodologies to overcome theselimitations.

In one or more embodiments of the present disclosure, rapid electrodeheating (e.g., about 1-120 sec; in some designs from about 1 to about 10sec; in other designs from about 10 to about 30 sec; in other designsfrom about 30 to about 60 sec; in other designs from about 60 to about120 sec) may advantageously be used on thick (e.g., in the range fromabout 60 micron to about 1200 micron), high areal capacity (e.g., 4.0 toabout 1000.0 mAh/cm²) electrodes. Very rapid solvent evaporation mayprevent or greatly minimize the formation of pore blockages (by thebinder) and/or may induce pore channels propagating perpendicular to theelectrode orientation, which may be beneficial in some designs formaximizing electrode rate performance. Several methodologies may beutilized to avoid drying the top of the electrode first.

In some designs, the electrode (or electrode slurry) may be rapidlyheated through contact heat transfer (conduction), where the bottom (orboth the bottom and the top) of the electrode gets in a direct contactwith hot object(s) (e.g., hot roll(s) or hot belt(s) or hot plate(s),etc.). The temperature of such objects may be very high (e.g., fromaround 80° C. to around 800° C.; in some designs, from around 80° C. toaround 140° C.; in other designs, from around 140° C. to around 200° C.;in other designs, from around 200° C. to around 300° C.; in otherdesigns, from around 300° C. to around 800° C.) and limited by thethermal or oxidation stability of the current collectors, electrodecomponents and the exposure time (higher temperature may typically beapplied for lower exposure time; please note that solvent evaporationcools down the electrode and its temperature may remain substantiallysmaller than that of the hot objects for some time). Since a slurrysolvent (e.g., water in some designs) needs pathways to escape, at leastthe top of the electrode may contact either (i) a porous object (whichmay be heated in some designs) and through these pores at least aportion (or most or all) of the slurry solvent (e.g., water, in somedesigns) may be removed or (ii) have no direct contact with any objectduring rapid heating (drying). In some designs, the electrode slurry maybe at least partially (e.g., partially, substantially or completely)dried so as to provide an at least partially dried electrode coating,which in some designs may comprise a residual amount of non-dried slurrysolvent. In some designs, the electrode slurry may be heated through thecurrent collector, another hot object, or a combination thereof. In somedesigns, an average temperature of the current collector and/or the hotobject during the drying may exceed about 200° C. (e.g., in somedesigns, from around 200° C. to around 300° C.; in other designs, fromaround 300° C. to around 800° C.) and limited by the thermal oroxidation stability of the current collector and electrode componentsand the exposure time (higher temperature may typically be applied forlower exposure time; please note that solvent evaporation cools down theelectrode and its temperature may remain substantially smaller than thatof the hot objects for some time). In some designs, the coating anddrying may be performed continuously (or semi-continuously), such as viaroll-to-roll continuous electrode densification.

In some designs, a series of two or more hot objects heated to differenttemperatures may be used in series in contact with the electrode inorder to effectively and rapidly dry the solvent, without over-heatingsome portion of the electrode, which may undesirably lead todegradation, oxidation or other unwanted outcomes. For example, thefirst hot object heated to a temperature T1 may dry majority of thesolvent, while the second hot object heated to a temperature T2 (e.g.,T2<T2) may further remove at least some of the remaining solvent withoutthe danger of over-heating the electrode and, for example, undesirablyreduce mechanical properties of the electrode coating or the binder orthe current collector, etc. In some designs, three, four or more hotobjects may be subsequently used. In some designs, a hot object (or aseries of hot objects) may be heated to gradually changing temperature.In some designs, more dried electrode may get in contact with a colderportion of a hot object.

In some designs, the bottom of the electrode may be heated to a highertemperature (e.g., by about 20-200° C. or even more) than the top of theelectrode during rapid drying. In some designs, only the bottom of theelectrode may be heated during rapid drying. In some designs, there maybe no contact of any object with the top of the electrode during rapiddrying.

In some designs, the hot object(s) in a direct contact with theelectrode may be electrically conductive. In some designs, the hotobject(s) in a direct contact with the electrode may be heatedresistively or inductively. In some designs, the hot object(s) in adirect contact with the electrode may comprise conductive carbon (e.g.,conductive carbon fibers, conductive carbon felt, conductive carbonfabric, graphite paper/sheet or graphene or conductive carbon nanotubes,etc.) or metals. In some designs, if metals are used in the design ofhot objects, they should be sufficiently corrosion resistant (e.g.,nickel-containing foils or sheets or mesh or felt may be used in somedesigns).

In some designs, mechanical pressure may be applied to the electrodeduring rapid drying (e.g., somewhere from around 0.01 atm to around 1000atm) to reduce or prevent small particles from escaping the electrodeupon rapid solvent evaporation or otherwise to enhance mechanicalintegrity of the electrode by mitigating some of the internal stressesin the electrode coating induced by rapid heating. In some designs, bothelectrode drying and electrode calendaring (densification) may beapplied at the same time.

In some designs, rapid electrode heating may be induced by resistiveheating (e.g., by passing the electric current either through thecurrent collectors or through the electrode or through the contactingobjects and their various combinations, in some designs). In somedesigns, the current can be passed from the current collector throughthe electrode perpendicular to the top electrically conductive contact.In some designs, primarily the current collector may be heated (e.g., byradiation, by induction, resistively or by a combination of differentapproaches).

In some designs, such heat may be supplied inductively or resistively tothe current collector and electrodes, similarly to the approachesdescribed above for improved calendaring.

Conventionally, copper current collectors are used for most of Li-ionbattery anodes and aluminum current collectors are used for most ofLi-ion battery cathodes. Unfortunately, exposing both Cu and Al toelevated temperatures for a prolonged period may undesirably affecttheir properties. For example, Cu and Al may exhibit lower strength andbecome softer after a heat-treatment induced by the rapid drying orcalendaring described in accordance with embodiments of the disclosure.The surface or grain boundaries within Cu may additionally corrode(oxidize) during exposure to high temperatures in the presence of wateror other slurry solvents or air. Several strategies may beadvantageously used in order to overcome some or all of suchlimitations. First, in some designs, a Cu current collector surface maybe advantageously coated with a protective surface layer (e.g., made ofconductive paint or a carbon layer or a metal or metal alloy (e.g., Ni)coating (e.g., electrodeposited or sputtered, etc.), etc.) which wouldprotect Cu from undesirable corrosion. Second, in some designs, acurrent collector foil may comprise a layered structure, where layers ofmore mechanically strong, more thermally stable and more corrosionresistant materials (e.g., Ni, Ti, etc. and/or their various alloys) arealtered with the layers of more electrically conductive materials (e.g.,Cu for anodes or Al for cathodes and some of the higher voltage anodes).Third, in some designs, a temperature and a time of the rapidheat-treatment during rapid drying (or calendaring) may be optimized tominimize such negative outcomes to below the acceptable (for a givenapplication and a given cell design) level. Fourth, in some designs, thecurrent collector(s) may be strain-hardened to a sufficiently high level(e.g., to reduce grain size, to introduce more dislocation and otherdefects in order to increase current collector strength at the expenseof reduced ductility) to account for the strain relaxation taking placeduring heating (which would increase their ductility to the acceptablelevel prior to assembling into cells). Fifth, in some designs, currentcollectors may be reinforced with nanoparticles or nanofibers, which mayreduce their grain growth rates in order to maintain higher strengthafter heating. Other mitigating strategies may also be utilized.

In some designs, water-based slurries may be advantageously used forelectrode (e.g., anode or cathode) formation (e.g., particularly whensubjected to rapid heating) as these are environmentally benign andbecause water is not flammable.

In other designs, solvents with latent heat of evaporation lower thanthat of water (e.g., by about 2 times or more) or solvents with asurface tension lower than water (e.g., by about 2 times or more) (orboth) or water-solvent mixtures may be used instead for the slurrycoating. The use of nonaqueous solvent(s) (or solvent-water mixtures)may reduce oxidation of some current collectors (e.g., Cu) during rapiddrying. The use of solvents with a lower heat of evaporation compared towater (in some designs, lower by about 2 times or more) may reduceenergy consumption of the drying process. The use of solvents with lowersurface tension than water (in some designs, lower by 2 times or more)may reduce stresses during drying and enhance mechanical properties orpore connectivity of the dried electrodes (e.g., particularly whensubjected to rapid heating). Illustrative examples of low surfacetension solvents include, but are not limited to, acetic acid, toluene,tetrahydrofuran, sym-tetrachloromethane, tert-butylchloride, propanol(methanol, ethanol, etc.), acetone, polydimethyl siloxane (baysilonem5), perfluoroheptane, perfluorohexane, perfluorooctane, nitroethane,undecane, octane, hexane, heptane, hexadecane (hdec), decane (dec),methyl ethyl ketone (mek), m-nitrotoluene, isobutylchloride,isoamylchloride, dichloromethane, dipropylene glycol monomethylether,decalin, p-cymene, cyclohexane, 1-decano, acetone (2-propanone),1-chlorobutane, 1,2-dichloro ethane, among others. However, in somedesigns, a careful design of the rapid heating apparatus may beconfigured to greatly minimize (or preferably eliminate) the probabilityof fires (e.g., by ignition of the solvents during rapid heating) (e.g.,utilizing designs with reduced O₂ content in the area where electrodesand solvents are exposed to elevated temperatures) and minimize theprobability of solvent vapors escaping the exhaust and solvent recoverysystem and endangering the safety or health of humans or animals in thevicinity (e.g., utilizing designs that explores the use of gas blankets,negative pressure, seals, cold walls/condensers and other methods). Insome designs, it may be preferable for the solvent to exhibit a flashpoint above around 21° C. and characterized as “flammable” (as opposedto “extremely flammable” and “highly flammable”) (in some designs, abovearound 50° C.; in some designs, above around 90° C.). In some designs,aqueous solution of solvents (mixture of solvents and water) may be usedto reduce their flammability or attain other benefits.

FIGS. 8A and 8B illustrate cross-sections of example slurry-castedelectrodes subjected to a rapid heating to evaporate the solvent inaccordance with embodiments of the disclosure.

In the illustrative example of FIG. 8A, a thick electrode coating 801cast on a current collector 802 is arranged in contact with porous hotobjects 803 on top/bottom sides of a current collector 802. In thisexample, the electrode (e.g., comprised of current collector 802 withtop/bottom electrode coatings 801 arranged thereon) is symmetric and hotobjects 803 touch both sides of the electrode. However, it will beappreciated that in some designs only one side of the electrode may becoated or only one side of the electrode may comprise a solvent.Transferring heat from the respective hot objects 803 to the respectivetop/bottom electrode coatings 801 quickly boils and evaporates thesolvent 804, which may escape through the pores of the hot objects 803,in some designs, and be exhausted, while creating pore channels withinthe electrode to minimize its tortuosity. In some designs, pressure maybe applied to the respective electrode coatings 801 from the respectivehot objects 803 during heating. In some designs, such a pressure may bedynamic. In some designs, such a pressure may help to densify anelectrode at the same time or avoid material losses or undesiredroughening of the electrode. In some designs, the average temperature onthe bottom of the electrode 803 near a current collector (Tb) may belower, the same or higher than the average temperature on the top (e.g.,the part of the electrode coating 801 further away from the currentcollector 802) of the electrode coating 801 near a respective hot object803 (Tt) during rapid heating and solvent evaporation. In some designs,it may be advantageous to heat the current collector 802 (with orwithout simultaneous heating the porous hot objects 803) in order toensure Tb is higher than Tt.

In an illustrative example of FIG. 8B, a thick electrode coating 801cast on a current collector 802 is rapidly heated by the currentcollector 802. In this case an average temperature of the currentcollector Tc may be higher than an average temperature of the bottom ofthe electrode Tb, which, in turn, may be higher than an averagetemperature of the top of the electrode Tt during the rapid solventevaporation. In this illustrative example of FIG. 8B, only one side ofthe electrode comprises a solvent that needs to be evaporated. In somedesigns, a porous object (not shown) may be in contact with asolvent-comprising electrode side in order to reduce surface rougheningor mass losses or to enhance electrode density or to provide otheruseful functions to the produced thick electrode.

FIG. 9 illustrates another example of a slurry-casted electrode 901subjected to a rapid heating to evaporate the solvent in accordance withan embodiment of the disclosure. In the illustrative example of FIG. 9,an electrode slurry 901 s is cast only on one side of a currentcollector 902. During rapid drying utilizing an example embodiment, theinitial electrode slurry 901 s becomes drier and denser 901 e after theelectrode slurry 901 s passes through a heated belt setup 904. Such asetup may have two sides touching both a coating side being dried andthe opposite side of the electrode (e.g., the current collector 902, ora pre-dried electrode side). During rapid drying the coating thicknessof the electrode slurry 901 s may gradually get reduced. Rollers 903 maybe used to move the electrode during drying and densification processes.Rollers 905, 906 and 908 may be used to move heated belt 907 t. In somedesigns, a potential difference between some of the conductive rollers(e.g., between the rollers 905 t and 906 t of one side of the heatedbelt setup or between the rollers 905 b and 906 b of another side of theheated belt 907 t setup or both) may be used to conduct the currentthrough one portion of the heated belt 907 t or the other portion of theheated belt 907 b or both, thereby heating it to the desiredtemperature. In some designs, the temperature of one side of the beltsetup that is in a direct contact with a solvent-comprising electrodeside (TBt) may be lower than the temperature (TBb) of the other side ofthe belt setup that is in a direct contact with the opposite side of anelectrode (e.g., a current collector 902, or a pre-dried electrodeside). In this case, the average temperature of the bottom of theelectrode Tb may be higher than an average temperature of the top of theelectrode Tt. In some designs, the heated belt 907 t that is in contactwith a solvent-comprising electrode side may be porous to enable slurrysolvent 909 to evaporate and be exhausted.

In conventional electrode fabrication, electrodes are fully dried beforecalendaring and before assembling into the jellyroll or stack forinsertion into the case (or pouch) and electrolyte filling. However, aspreviously described drying thick (e.g., about 60-1200 micron), highloading (e.g., about 4.0 to about 1000.0 mAh/cm²) electrodes may induceundesirable stresses and defects, which may undesirably reduce cohesionor adhesion to the current collector or may undesirably increasetortuosity, thus resulting in reduced rate performance or stability orboth. Some aspects of the present disclosure provide mechanisms andmethodologies to overcome these limitations.

In some designs, not fully drying the electrode and retaining a fractionof the slurry (electrode paste) solvent (e.g., leaving from around 0.5vol. % to around 25 vol. % solvent relative to the total final electrodevolume; in some designs from around 0.5 vol. % to around 5 vol. %; inother designs from around 5 vol. % to around 15 vol. %; in other designsfrom around 15 vol. % to around 25 vol. %) after partial drying or (insome designs) even after calendering (electrode densification) mayadvantageously enable lower tortuosity and substantially reduced tensilestresses that may enable better rate performance or better stability ofcells. In some designs, calendering may be conducted at room temperatureor at moderate temperatures (e.g., about 20-60° C.) on these not fullydried electrodes. In some designs, the slurry solvent may comprise acomponent of the electrolyte (e.g., a carbonate or an ether or asulfone, etc., which may be fluorinated in some designs). In this casethe not fully dried electrode(s) and the separator may be assembled intosandwich stacks or jelly rolls, inserted into a pouch or a case andfilled with the remaining components of the electrolyte prior toformation and using the cells. In some designs, the slurry solvent maycomprise a component of the electrolyte that is solid at near roomtemperature (has a melting point above or around 20° C.). For example,ethylene carbonate (EC), a very common and suitable component of theLi-ion battery electrolytes has a melting point of about 34 to about 37°C. and may be made part of the slurry solvent. Other common and suitablehigh-melting point electrolyte solvents include, but are not limited to:vinylene carbonate (VC, melting point 22° C.),4-Fluoro-1,3-dioxolan-2-one (FEC, melting point 18-23° C.), vinylethylene carbonate (VEC, melting point 22° C.), ethyl methyl carbonate(EMC, melting point 26-27° C.), to name a few. In some designs, thesolvent of the electrode slurry may comprise a mixture of two and moresolvents with distinctly different melting points (e.g., by about20-200° C.) and vapor pressures (e.g., by about 2-20,000 times at about60-200° C.). In some designs, one or more solvent of the electrodeslurries may preferentially evaporate, leaving (e.g., majority of) oneor more other solvents in the not fully dried electrodes prior tocalendaring or prior to cell assembling.

FIG. 10 illustrates a method of cell manufacturing with at least one notfully dried electrode in accordance with an embodiment of thedisclosure. In this illustrating example, a suitable slurry of suitablethickness is first cast on a current collector (1001). This slurry isthen only partially dried, leaving a suitable portion of the electrodeslurry solvent (or a portion of the initial mixture of slurry solvents)distributed within the pores of a thick electrode (1002). The presenceof such remaining solvent reduced internal stresses within the electrodeduring partial drying, which may improve its properties. The producedthick, high-loading electrode may then optionally be calendered (furtherdensified, 1003). In some designs, calendaring may be done hot or cold.In some designs, dynamic force may be applied during calendaring. Insome designs, at least a portion of the remaining solvent may remain inthe electrode after calendaring. The presence of such remaining solventmay prevent or greatly reduce formation of closed or highly torturouspores. The electrode stack or jellyroll may then be assembled where atleast one electrode (e.g., an anode or a cathode or both) may compriseremaining solvent and enclosed within a rigid or solid cell case (orpouch) (1004). At room temperature, such a solvent may be in a solidstate (e.g., if it exhibits a melting point above a room temperature).The cell then may be filled with electrolyte miscible with a remainingsolvent to form a desired electrolyte composition and may be sealed (orpre-sealed) (1005). Finally, the cell may optionally be subjected to aformation cycle at the desired temperature (e.g., in some designs, underpressure), degassed and fully sealed to form a high-performance (e.g.high-rate or high stability or low temperature performing) cell withhigh-loading electrodes (1006).

FIG. 11A-11E illustrate exemplary formation of a building block of acell with thick, high loading electrodes produced according to one ofthe embodiments of the present disclosure. FIG. 11A illustratesexemplary slurry 1100A comprised of active particles 1101, conductiveadditives 1103 and an initial solvent 1102 i, which may additionallycomprise a dissolved or dispersed binder 1104, cast on a currentcollector 1105. FIG. 11B illustrates a slurry 1100B after partiallydrying of the slurry 1100A and forming a layer of active materials 1101intermixed with conductive additives 1103 and binder 1104 coated on acurrent collector 1105, where an intermediate portion 1102 i of thesolvent (or a portion of the initial solvent mixture) remains in thepores of the coated layer. FIG. 11C illustrates a coating 1100C afterdensification (calendering; in some designs conducted at elevatedtemperatures and in some designs conducted at near room temperature; insome designs produced by dynamic loading) of the slurry 1200B, wheredensely packed active material particles 1101 are intermixed withconductive additives 1103 and binder 1104 coated on a current collector1105, where a final portion 1102 f of the solvent (or a portion of theinitial solvent mixture) remains in the pores of the coated layer. FIG.11D illustrates a repeat unit stack 1100D of a battery cell with highloading electrodes, where at least one of the electrodes (in thisexample, a cathode) comprises some of the solvent in its pores. Here,the anode current collector 1105 a is coated with anode active materials1101 a mixed with conductive additives 1103 a and a binder; the cathodecurrent collector 1105 c is coated with cathode active materials 1101 cmixed with conductive additives 1103 c and a binder and where solvent1102 f remains in at least a portion of the cathode pores. The anode andthe cathodes are electrically separated with a porous separator 1106.FIG. 11E illustrates a repeat unit stack 1100E of a battery cell withhigh loading electrodes produced by filling the pores remaining in theunit stack of 1100D of the FIG. 11D with an electrolyte miscible with asolvent 1102 f to produce a final electrolyte composition 1107.

In some designs, various disclosed embodiments of thick electrodedrying, thick electrode calendaring or using not fully dried thickelectrodes in cell construction may be either utilized separately oradvantageously combined.

Some aspects of this disclosure may also be applicable to electrodeswith medium capacity loadings (e.g., in the range from around 2 toaround 4 mAh/cm²).

High capacity, high energy batteries (e.g., cells with energy density inexcess of around 10 watt-hours (Wh); preferably in excess of about 15Wh; in some designs, in excess of about 30 Wh; in some designs, inexcess of about 100 Wh; in some designs, in excess of about 200 Wh) mayparticularly benefit from various aspects of this disclosure becausesuch batteries are typically harder to dry and produce and may sufferparticularly strongly from the above-discussed limitations of certainconventional methodologies.

High-energy density Li-ion batteries (e.g., cells with energy density inexcess of about 600 Wh/L; in some designs in excess of about 700 Wh/L;in other designs in excess of about 800 Wh/L; in other designs in excessof about 900 Wh/L; in other designs in excess of about 1000 Wh/L) withhigh-areal loading electrodes may particularly benefit from variousaspects of this disclosure because such batteries are typically harderto dry and produce and may suffer particularly strongly from theabove-discussed limitations of certain conventional methodologies(including, but not limited to low rate performance or fast degradationor both).

High-power density Li-ion batteries (e.g., cells with power density inexcess of about 1000 Wh/L; in some designs in excess of about 1600 Wh/L;in other designs in excess of about 3000 Wh/L, when measured at around40° C.) particularly with high-areal loading electrodes (e.g., about 4mAh/cm²) may particularly benefit from various aspects of thisdisclosure because such batteries are typically harder to dry andproduce and may suffer particularly strongly from the above-discussedlimitations of certain conventional methodologies.

Li-ion battery cells that require fast charging (e.g., wherein the cellmay be charged from around 10% state of charge to around 80% state ofcharge within about 20-30 min or less (in some designs within about 15min or less) when charged at around 40° C.) particularly with high-arealloading electrodes (e.g., 4 mAh/cm²) may particularly benefit fromvarious aspects of this disclosure because such batteries are typicallyharder to dry and produce and may suffer particularly strongly from theabove-discussed limitations of certain conventional methodologies.

Li-ion battery cells that require fast discharging (e.g., wherein thecell is configured to discharge about 80% or more of its maximum storedenergy within about 20 minutes or less when discharged at around 40° C.)particularly with high-areal loading electrodes (e.g., 4 mAh/cm²) mayparticularly benefit from various aspects of this disclosure becausesuch batteries are typically harder to dry and produce and may sufferparticularly strongly from the above-discussed limitations of certainconventional methodologies.

Li-ion batteries comprising conversion-type anode materials, such asalloying-type anode materials (such as those comprising Si or Lialloying elements) or Li metal anodes, may particularly benefit fromvarious aspects of this disclosure because such batteries may becomecathode-limited in performance and thickness. In some designs, Si mayadvantageously be a part of the composite particles. In some designs,the weight fraction of Si may range from around 5 wt. % to around 80 wt.% as compared to the total weight of the electrolyte-free electrode(e.g., anode) coating (not counting the weight of the currentcollector). In some designs, it may be advantageous for the anode tocomprise carbon in order to enhance its electrical conductivity, enhanceits mechanical properties or provide other benefits. In some designs,the electrode (e.g., anode) may comprise silicon (Si), carbon (C), or acombination of Si and C. In some designs, the electrode (e.g., anode)may comprise Si-containing composite (e.g., nanocomposite) particles.

Li-ion batteries comprising dense electrodes (e.g., anodes with porosityof less than around 30 vol. %; in some designs less than around 20 vol.%; in some designs less than around 15 vol. %; or cathodes with porosityof less than around 20 vol. %; in some designs less than around 15 vol.%; in some designs less than around 10 vol. %) particularly withhigh-areal loading electrodes (e.g., 4 mAh/cm²) may particularly benefitfrom various aspects of this disclosure because such batteries aretypically harder to dry and produce and may suffer particularly stronglyfrom the above-discussed limitations of certain conventionalmethodologies.

Li-ion batteries comprising thick electrodes (e.g., wherein the averagethickness of the one side of the densified electrode coating ranges fromaround 60 to around 800 micron, not considering the thickness of thecurrent collector) may particularly benefit from various aspects of thisdisclosure because such batteries are typically harder to dry andproduce and may suffer particularly strongly from the above-discussedlimitations of certain conventional methodologies.

Electrode coating and drying or electrode densification conducted onsuitable electrode materials according to methodologies and toolsdescribed in various aspects of this disclosure may become particularlyattractive if it is conducted continuously (or semi-continuously), suchas via roll-to-roll continuous electrode densification.

This description is provided to enable any person skilled in the art tomake or use embodiments of the present invention. It will beappreciated, however, that the present invention is not limited to theparticular formulations, process steps, and materials disclosed herein,as various modifications to these embodiments will be readily apparentto those skilled in the art. That is, the generic principles definedherein may be applied to other embodiments without departing from thespirit or scope of the invention.

1. A Li-ion battery cell, comprising: anode and cathode electrodes; anelectrolyte ionically coupling the anode and the cathode electrodes; anda separator electrically separating the anode and the cathodeelectrodes, wherein the anode and cathode electrodes comprise at leastone densified electrode exhibiting an areal capacity loading of morethan about 4 mAh/cm² and comprising a first electrode part arranged on acurrent collector and a second electrode part on top of the firstelectrode part, the second electrode part of the at least one densifiedelectrode having a higher porosity than the first electrode part of theat least one densified electrode.
 2. The Li-ion battery cell of claim 1,wherein the anode electrode comprises silicon (Si), carbon (C), or acombination of Si and C.
 3. The Li-ion battery cell of claim 2, whereinSi in the anode electrode ranges from around 5 wt. % to around 80 wt. %.4. The Li-ion battery cell of claim 2, wherein the anode electrodecomprises Si-containing composite particles.
 5. The Li-ion battery cellof claim 1, wherein a total energy that may be stored in the Li-ionbattery cell exceeds about 10 Wh.
 6. The Li-ion battery cell of claim 1,wherein a volumetric energy density of the Li-ion battery cell exceedsabout 600 Wh/L.
 7. The Li-ion battery cell of claim 6, wherein thevolumetric energy density of the Li-ion battery cell exceeds about 800Wh/L.
 8. The Li-ion battery cell of claim 1, wherein a volumetric powerdensity of the Li-ion battery cell exceeds about 1600 W/L when measuredat around 40° C.
 9. The Li-ion battery cell of claim 1, wherein theLi-ion battery cell is configured to discharge about 80% or more of itsmaximum stored energy within about 20 minutes or less when discharged ataround 40° C.
 10. The Li-ion battery cell of claim 1, wherein the Li-ionbattery cell is configured charge from around 10% state of charge toaround 80% state of charge within about 20 minutes or less when chargedat around 40° C.
 11. A densified electrode for a Li-ion battery,comprising: a first electrode part arranged on a current collector; anda second electrode part arranged on top of the first electrode part, thesecond electrode part having a higher porosity than the bottom electrodepart, wherein the densified electrode exhibits an areal capacity loadingin excess of about 4 mAh/cm².
 12. The densified electrode of claim 11,wherein an average thickness of the densified electrode ranges fromaround 60 micron to around 800 micron.
 13. The densified electrode ofclaim 11, wherein an average porosity of the densified electrode isbelow around 20 vol. %.
 14. A method of fabricating an electrode,comprising: coating a current collector with a set of electrode layersso as to define a first electrode part arranged on the current collectorand a second electrode part arranged on top of the first electrode part;and densifying the set of electrode layers after the coating via apressure roller to produce a densified electrode while maintaining acontacting part of the pressure roller at a temperature that is lessthan a temperature of the second electrode part.
 15. The method of claim14, wherein the temperature of the current collector exceeds thetemperature of the contacting part of the pressure roller by around 20°C. or more.
 16. A method of fabricating an electrode for a Li-ionbattery, comprising: coating a current collector with one or moreelectrode layers; and densifying the one or more electrode layers afterthe coating via applying a time-varying pressure to produce a densifiedelectrode.
 17. The method of claim 16, wherein an average amplitude ofthe time-varying pressure during the densifying ranges from around 1% toaround 50% of the maximum pressure.
 18. The method of claim 16, whereinthe time-varying pressure is modulated in accordance with a definedfrequency or range of frequencies.
 19. The method of claim 18, whereinthe frequency of the time-varying pressure modulation ranges from around0.1 Hz to around 10 MHz.
 20. The method of claim 16, wherein thedensifying comprises roll-to-roll continuous electrode densification.21. A method of fabricating an electrode for a Li-ion battery,comprising: coating a current collector with an electrode slurrycomprising at least active electrode particles and a solvent; anddrying, during a drying time, the electrode slurry to produce an atleast partially dried electrode coating, wherein the drying time rangesfrom around 1 to around 120 seconds.
 22. The method of claim 21, whereinthe drying comprises: heating the electrode slurry through the currentcollector, another hot object, or a combination thereof.
 23. The methodof claim 22, wherein an average temperature of the current collectorand/or the hot object during the drying exceeds about 200° C.
 24. Themethod of claim 21, wherein the drying comprises: applying a pressure tothe electrode slurry.
 25. The method of claim 21, wherein the coatingand drying is performed continuously.